The present invention relates to the recovery of tungsten from heavy metal alloys. Heavy metal alloys are extensively used as shields or containers for radio active materials, as gyroscope rotors, counterweights, and corrosion resistant parts for jet air craft, and as armor penetrating projectiles and rocket nose cones.
Such alloys are dense, hard and corrosion resistant. Due to their nature, recovery of various valuable metal components is difficult. Typical recovery methods employing conventional acids, bases of other solvents are generally slow, expensive and otherwise generally ineffective from the standpoint of a commercial operation. U.S. Pat. No. 2,716,558 to Hall describes a process for recovering nickel and copper from Monel metal by introducing the alloy into an aqueous solution of strong inorganic acid, e.g. sulfuric nitric or hydrochloric acid and passing sulfur dioxide into the solution. According to this process, dissolution of the metals is slow and resulting gases are highly toxic and undesirable.
Other methods have been found impractical. For instance, acid leaching of heavy metal by hot hydrochloric acid was exceedingly slow. A cylinder approximately four inches in diameter by eight inches long was only leached to the depth of one quarter inch after thirty days using concentrated hot, hydrochloric acid at a temperature of 110.degree. C. The use of oxidizing acids, such as nitric acid, also oxidize the tungsten producing tungsten oxide. It was also discovered that the fusion of heavy metals in sodium hydroxide is also very slow. A fifty gram piece requires sixteen hours for complete dissolution at 1000.degree. C.
U.S. Pat. No. 3,595,484 to Barnard relates to a process for the reclamation of tungsten carbide from cemented carbides by treating the cemented carbide with molten zinc and subsequently distilling the zinc from the mass. The zinc forms an alloy with cementing agent, usually cobalt, thereby dissolving the cementing agent and permitting recovery of a mixture of the carbide and cementing agent in a form that can be reused in the preparation of cemented carbides.
British Pat. No. 582,921 relates to the recovery of refractory carbides by treatment of a scrap molten zinc and subsequently leaching the resulting alloy with an acid solution followed by recovery of products from the solution.
It is an object of the present invention to provide a process for rapidly and economically effecting the recovery of tungsten from heavy metal alloys in such a form that the tungsten may be reused to form new articles.
Other and further objects of the present invention will become apparent from reading the following description.
In accordance with the present invention, there is provided a method for reclaiming tungsten from heavy metal alloys comprising treating the heavy metal alloy with molten zinc for a sufficient period of time and at a sufficient temperature to form a resulting alloy comprising zinc and tungsten separating the zinc from the resulting alloy comprising zinc and tungsten.